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A comparison of two methods for studying the diet of the peregrine falcon

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... However, small-to medium-size prey could be overestimated in pellet contents as well as large prey in prey remains (see Sect. 4.2.2;Mearns 1983;Oró and Tella 1995). DNA-based molecular methods on prey remains can reveal new prey species and assure the absence of less frequent and/or underestimated prey such as amphibians, reptiles, and mammals (Han and Ho 2018). ...
... Falcons with 10-60% avian prey should be considered as mammalian-eaters, and those with 60-100% are bird-eater birds ). (Data from Ratcliffe 1962;Cade et al. 1968;Sherrod 1978;Frey and Senn 1980;Aubry 1982, Frumkin andPinshow 1983;Burnhan and Mattox 1984;Ristow et al. 1986;Bradley and Oliphant 1991;Aspinall 1996;Horák 1998;Bagyura et al. 1994;Oró and Tella 1995;Obuch and Chavko 1997;Gombobaatar et al. 2001;Watson and Clarke 2000;Rejt 2001;Serra et al. 2001;Carter et al. 2003;Bagyura et al. 2004;Rizzolli et al. 2005 Falcons show a certain dietary plasticity due to environmental conditions that limit distribution of prey and their abundances. For example, peregrine falcons in temperate areas are relatively specialized feeders, whereas they appear to become more generalized in extreme environments such as deserts, taiga, and tundra (Jenkins and Avery 1999). ...
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Falcons show fine anatomical and physiological adaptations to capture different kinds of prey, but the mean prey mass correlated positively with mean mass of the falcon. The proportion of birds affect the diet breadth at species level, and the proportion of invertebrates negatively correlate with the rate of mammals. Thus, mammalian-eating falcons able to switch to alternative prey, and bird-eating falcons are forced to enlarge their foraging area to find enough avian prey. Ultimately, prey size and the type of prey increase the reversed size dimorphism (RSD) of falcons from insects to mammals to birds as prey. Falcons show a certain dietary plasticity due to environmental conditions that limit the distribution of prey and their abundances. The food composition can differ significantly depending on the season and falcons adjusted hunting efforts and techniques accordingly. In addition, the breadth of the food niche was positively correlated with habitat heterogeneity that ultimately increases the number of prey species, especially birds. Hunting techniques adopted by falcons depend on prey size and prey type, and their availability is mainly related to variable environmental factors. Anyway, they prioritize saving energy when foraging than time spent during foraging bouts. Avian predators are one of the major factors modifying avian and mammalian prey assemblages of a territory. Spatial synchrony in rodent population fluctuation is well described at boreal ecosystem and also in Central Europe but at a large spatial scale. Falcons that exclusively exploit migrating small birds for rearing young need to move to their breeding areas every year and then leave these areas outside the breeding season due to the absence of alternative prey out the seasonal migration periods. Flocking, vigilance, and mobbing are adopted by prey against falcons’ attacks, but hunting success of falcons is highest in attacks on small flocks. Populations of specialist predators often fluctuate with populations of preferred prey species. For example, stable, regular, synchronous, 10–12-year quasi-cycles have been demonstrated in grouses and gyrfalcons.
... Most of the literature on rap- tor food habits derives from methods known to be biased (namely, pellet analyses and prey remains from eyries; Sherrod 1978). Some studies have even relied only on materials collected at the base of breeding cliffs (Oro and Tella 1995). Prey remains sometimes adequately document the proportion of each prey species in the diet of certain raptors (e.g., Collopy 1983, Golden Eagle [Aquila chrysaetos]). ...
... Insects are seldom reported as food items in peregrine prey studies, but Snyder and Wiley (1976) estimated that insects represented 20% of the diet (by number) in a sample of 116 stomachs. Also, Oro and Tella (1995) found arthropod remains important in pellets, but not in prey remains, under eyries in Spain, and Ritchie (1982) reported insects in the diet of Alaskan peregrines. Dekker (1999) concluded that insects are commonly taken by recently fledged peregrines. ...
Article
We collected prey remains from 25 Peregrine Falcon (Falco peregrinus) territories across Arizona from 1977 to 1988 yielding 58 eyrie-years of data. Along with 793 individual birds (107 species and six additional genera), we found seven mammals and nine insects. In addition, two nestling peregrines were consumed. We found a larger dependence upon White-throated Swifts (Aeronautes saxatalis) and birds on migration in northern Arizona, while in southeastern and central Arizona average prey mass was greater and columbiforms formed the largest dietary component. In northern, central, and southeastern Arizona, 74, 66, and 56 avian prey taxa, respectively, were recorded. We used capture-recapture modeling to estimate totals of 111 ± 9.5, 113 ± 10.5, and 86 ± 7.9 (SE) avian taxa taken in these same three areas. These values are counterintuitive inasmuch as the southeast has the richest avifauna. For the entire study area, 156 ± 9.3 avian taxa were estimated to be taken by peregrines. Dieta Estival de Falco peregrinus en Arizona Comparando Zonas Ricas y Pobres en Avifauna Mediante un Modelo de Captura-Recaptura Resumen. Desde 1977 a 1988 colectamos restos de presas en 58 nidos de Falco peregrinus a través de Arizona. Conjuntamente con 793 aves individuales (107 especies y seis géneros adicionales), encontramos siete mamíferos y nueve insectos. Además, fueron consumidos dos pichones de Falco peregrinus. En la zona norte encontramos una mayor dependencia sobre Aeronautes saxatalis y aves en migración, mientras que en las zonas sureste y central la masa promedio de presa fue más grande y los columbiformes constituyeron el componente principal de la dieta de Falco peregrinus. En las zonas norte, central y sureste se registraron 74, 66 y 56 taxa de aves presa, respectivamente. Para estimar el número total de taxa capturados por Falco peregrinus usamos un modelo de captura-recaptura. Los valores calculados fueron 111 ± 9.5, 113 ± 10.5 y 86 ± 7.9 (EE) taxa para las zonas norte, central y sureste, respectivamente. Estos valores no reflejan los que esperábamos, ya que la zona sureste tuvo una avifauna más rica. Se estimó que 156 ± 9.3 taxa fueron capturados por Falco peregrinus en la totalidad del área de estudio.
... Methods used to study raptor diets vary depending on the study species and resources available to the researcher. Traditional methods include collecting prey remains (McPherson et al. 2016, Suri et al. 2017 and/or pellets (Oro & Tella 1995, Šalek et al. 2010, Sumasgutner et al. 2013, radio-telemetry (Kenward 1982, Rutz 2003, cameras or hides (Newton 1978, Murgatroyd et al. 2016, Harrison et al. 2019, and, more recently, satellite-telemetry (Arkumarev et al. 2021), stable isotope analyses (Catry et al. 2016, Johnson et al. 2020, Jones et al. 2023, DNA metabarcoding (Bourbour et al. 2019(Bourbour et al. , 2021, and websourced photography (Naude et al. 2019, Berryman & Kirwan 2021, Panter & Amar 2021. Long-term direct field observations, by experienced observers, allow for repeated visits to known territories over time (Snyder & Wiley 1976, Collopy 1983 and are a suitable method for studying species whose pellets do not provide accurate representations of their diet (Marti 1987, Redpath et al. 2001. ...
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Capsule: Red-necked Falcons Falco chicquera shift their trophic niche, from eating birds to bats, during the rainy monsoon season. Aims: To explore seasonal changes in prey weight, diet composition, and mobbing interactions of the globally Near Threatened Red-necked Falcon in Bangladesh. Methods: We analysed long-term direct observations of 19 adult pairs feeding on prey between2002 and 2019, exploring changes in mean prey weight, prey group, and mobbing interactions throughout the cool dry winter, hot pre-monsoon, and rainy monsoon seasons. Results: The probability of bats being present within the diet increased over time, from 16% in the cool dry winter and 11% in the pre-monsoon hot season, to 48% in the rainy monsoon season. This coincided with a significant decline in mean prey weight and biomass consumed during the rainy monsoon season. Probabilities of falcons being mobbed during feeding varied throughout the seasons, depending on mobbing species. Conclusion: Red-necked Falcons appeared to track changing environments by shifting their trophic niche during the rainy monsoon season. This may be due to: (a) an optimal foraging response to bat population fluxes, itself a response to weather-induced increases in flying insect abundances, (b) opportunistic hunting of bats during periods of crepuscular activity peaks, and/or (c) the energetic demands of fledglings during the rainy monsoon season.
... Whenever possible, remains were identified to species level using our reference collections of bones and feathers or field guides (Jenni & Winkle 1994, Svensson et al. 2010, Demongin 2016. Prey remains and pellet data from each locality were combined (Oro & Tella 1995) to calculate the minimum number of individuals and their relative importance in terms of biomass, using the weight data given by Snow & Perrins (1998). For Barolo's Shearwater Puffinus baroli, weights were obtained from Bécares et al. (2015), while for the Plain Swift Apus unicolor and the Atlantic Canary Serinus canaria we used unpublished data obtained during ringing on Tenerife (n = 4 and n = 140, respectively; D. P. Padilla pers. ...
... Analyses of pellets and food remains are the most common methods to study bird diet, despite their limitations and biases, linked to prey sizes or digestibility 69,70 . However, colleting both (pellets and prey remains) may reduce these biases 71 . Collections were made twice in nests occupied by individuals that were previously marked with colour-numbered plastic rings to have information across years for the same breeding pairs (see 9 for details on the long-term burrowing owls monitoring program in the study area). ...
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Urbanization has reshaped ecosystems and changed natural processes, driving an intense transformation of biomes, biotic community composition and diversity. Despite the growing interest in studying urban ecology over the last decades, the consequences of these changes on species occupying these ecosystems are not yet fully understood. Trophic generalism and tolerance to human disturbance have been proposed as two key traits in the colonization of urban environments. However, most studies focused on species’ average traits, paying less attention to the potential role of inter-individual variability. Here, we examined diet specialization in urban and rural breeding pairs, as well as its relationship with individual behaviour and intraspecific competition, using the burrowing owl as a study model. Our results show that both urban and rural breeding pairs behaved as trophic specialists. The diet of burrowing owl breeding pairs followed a gradient from coleopteran- to micromammal-dominated, which is related to individual behaviour (bolder individuals consuming more coleopterans than shyer ones). Besides, pairs distant from others showed a more diverse diet than those experiencing higher levels of intraspecific competition. Models fitted separately for each habitat showed that the proportion of micromammals in the diet of urban breeding pairs was related to their behavior, while the diet of rural pairs was not affected by individual behavior but by intraspecific competition. However, despite the strong selection of tame and more explorative individuals in urban environments and the higher density they reach in this habitat type, they did not differ in their degree of diet specialization from rural conspecifics. Although it would be necessary to evaluate prey availability on a small scale, our results suggest that burrowing owl breeding pairs behave as specialists, despite the generalist character of the species, and that this specialization is not affected by the occupation of urban environments but to individual behaviour and intraspecific competition.
... A number of studies have demonstrated that the utilization of an unique food sampling method to describe quantitatively bird of prey diets may give highly biased results (e.g., Mearns 1983, Mersmann et al. 1992, Oro and Tella 1995, Redpath et al. 2001. Pellets have been suggested as the less biased source of information on diet because many prey species occurring in pellets are seldom found in prey remains (e.g., Simmons et al. 1991, Real 1996. ...
Article
The diet of the American Kestrel (Falco sparverius) and Aplomado Falcon (Falco femoralis) was quantified by analysis of their pellets during the summer 1997-1998 in an agricultural area of Araucanía, southern Chile. By number, the most important prey of the American Kestrel were insects (61% of all individual prey) followed by birds (23%), rodents (13.7%) and reptiles (2.6%). Avian prey accounted for the highest biomass contribution (79.6%), followed by rodents (18%). Biomass contribution of insects and reptiles was negligible. Birds were the staple prey of the Aplomado Falcon both by number (89%) and biomass (99%). Number and biomass contribution of rodent and insect prey was minute. Diet of both raptor species did not broadly overlap. Both the American Kestrel and Aplomado Falcon appeared to respond in an opportunistic manner to the most abundant bird prey in the field (Sicalis luteola), although the latter species could be consuming preferentially larger-sized avian prey.
... They may also take longer to consume, and previously we have estimated that in relation to small prey items, our method may over-represent large and medium prey items by 25% and 72%, respectively (see [21] for details). However, other methods of studying raptor diet, such as analysis of prey remains, are also known to be biased toward larger prey and mammals over birds, as such items are more likely to be detected [21,22,59]. ...
Article
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Traditional methods to study raptor diet are usually limited temporally, e.g., prey remains at nesting sites, and are unsuitable to examine dietary changes throughout the year. Using web-sourced photography, we explore temporal patterns in prey size and key prey species between sexes of the sexually dimorphic Eurasian Sparrowhawk (Accipiter nisus) throughout the United Kingdom. We examined 666 photographs of sparrowhawk on prey and identified the prey species involved, together with sparrowhawk sex. Changes in prey size and proportions of key prey species over time (seasonally and monthly) were explored for each sex. Prey weight was substantially higher for females than males. However, on average, prey size for both sexes declined during the summer period (May-June) being the lowest in June which is the main nestling-rearing month for both sparrowhawks and their prey. Compared to summer, Rock Doves (Columba livia) were more important prey for female sparrowhawk in winter. Whereas, for males, Eurasian Blackbirds (Turdus merula) were more important in spring compared to autumn. Web-sourced photography can overcome several limitations of previous methods used to study raptor diet including the ability to quantify diet between the sexes throughout the entire year, however, may also introduce a prey-size bias towards larger prey items.
... This bias may influence some of our results, due to Sparrowhawk sex and age groups differing in their apparent consumption of prey size classes. However, other methods exploring diet, such as the analysis of prey remains, are also known to be biased toward larger prey items and mammals over birds, as such prey items are more likely to be detected than smaller prey (Oro & Tella 1995, Redpath et al. 2001. ...
Article
Diet differences between the sexes and ages have often been recorded for bird species. Many raptor species show extreme sexual size dimorphism with females often considerably larger than the males and these differences may be reflected in their diets. Diet studies in raptors most frequently focus on analysing prey remains or pellets collected at nest sites. These methods are subsequently limited to breeding birds in the breeding season, and are also restricted by their inability to distinguish prey items between the sexes. The use of web‐sourced photographs to examine raptor diet has the potential to overcome some limitations of more traditional methods used to assess diet. We used this approach for the Eurasian Sparrowhawk Accipiter nisus in the United Kingdom, exploring diet between the sexes and ages throughout the entire year. In total, we obtained 843 web‐sourced photographs of sparrowhawks with their prey items. There were 12 key prey items that had a frequency ≥10 in the sparrowhawk diet: Common Wood Pigeon Columba palumbus, Common Starling Sturnus vulgaris, Eurasian Collared Dove Streptopelia decaocto, Rock Dove Columba livia, Common Blackbird Turdus merula, House Sparrow Passer domesticus, unidentified ‘small’ and ‘medium’ birds, European Goldfinch Carduelis carduelis, European Greenfinch Chloris chloris, Eurasian Blue Tit Caeruleus caeruleus and Stock Dove Columba oenas. Several prey species were more often seen in the diet of one sex or age group. Overall average prey weights of adult females were two and a half times heavier than adult males and one and a half times heavier for juvenile females. However, this method may be slightly biased towards larger prey items, which should be considered in future studies. Despite this limitation our method has enabled dietary differences between the sexes and ages of this highly sexual sized dimorphic raptor species to be explored throughout the year.
... Sheep and goat bones were pooled together in a sheep-goat category due to the difficulty of separating the bones of both species. Although the identification of nest remains may present some biases (i.e. in particular due to the underestimation of food items consisting of soft tissues of large animals; Oro and Tella, 1995), it is considered as a valid procedure widely used to characterize the Egyptian vulture diet elsewhere (e.g. Margalida et al., 2012a;Milchev et al., 2012;Dobrev et al., 2015). ...
Article
Food is a primary factor driving animal population dynamics. Low quality food (e.g. poisoned carrion) has caused large declines of Asian and African vulture populations pushing some species to the brink of extinction. Although Europe emerges as a stronghold for the guild, European vultures face potential food shortages due to sanitary restrictions banning the disposal of livestock carcasses in the field after the Bovine Spongiform Encephalopathy (BSE). Determining the diet of European vultures and in particular the role livestock plays in it is needed for preserving these species and their scavenging role in food webs. We analysed the diet composition of 13 nests of the endangered Egyptian vulture (Neophron percnopterus) in a species stronghold in Europe (NW Spain), during the period of BSE restrictions (2007, 2009 and 2010). We identified 312 remains from 25 species, mainly mammals (70.8%), birds (17.0%) and fishes (7.7%). Livestock dominated the Egyptian vulture diet, comprising 23.9% of total items (11.8% of sheep-goat, 7.0% of bovine). Differences in diet composition among nests responded to habitat characteristics determining the availability of some food items (e.g. water for fishes). Our findings support a major role of livestock in the Egyptian vulture diet, suggesting a lack of compliance with sanitary restrictions banning the disposal of livestock carcasses in the field, with potential to affect vulture conservation and their scav-enging function in ecosystems.
... Whenever possible, remains were identified to species level using our reference collections of bones and feathers or field guides (Jenni & Winkle 1994, Svensson et al. 2010, Demongin 2016. Prey remains and pellet data from each locality were combined (Oro & Tella 1995) to calculate the minimum number of individuals and their relative importance in terms of biomass, using the weight data given by Snow & Perrins (1998). For Barolo's Shearwater Puffinus baroli, weights were obtained from Bécares et al. (2015), while for the Plain Swift Apus unicolor and the Atlantic Canary Serinus canaria we used unpublished data obtained during ringing on Tenerife (n = 4 and n = 140, respectively; D. P. Padilla pers. ...
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During 2015 and 2016, we conducted the first systematic study of the size of the breeding population, distribution, habitat and diet of the Barbary Falcon Falco peregrinus pelegrinoides on La Palma, Canary Islands. We found a minimum of 28 territories (3.9 territories/100 km2) at an average distance of 3.6 km (range 1.7–7.7 km) from their nearest neighbours. The territories were distributed throughout the island, but there were more in the northern half, probably due to a greater availability of large cliffs. Falcons selected high cliffs situated in scrub-covered areas close to the coast with relatively high levels of human infrastructures. However, this picture could be biased due to the inherent difficulties in surveying the rugged innermost parts of the island, where some territories may not have been detected. The nine monitored nests were situated in natural cavities or ledges at heights ranging from 35 to 110 m above ground level. Egg-laying probably takes place in late March, later than in the rest of the Canarian archipelago, perhaps due to the rainier climate of this island. On average, almost two chicks fledged per nest, a similar rate to nearby populations. Diet was composed of at least seven bird species, with Columba livia being the most frequently hunted and the most important prey item (93.9% of diet biomass). As falcons prey upon domestic racing pigeons (a popular activity on the island), direct persecution could be one of the main threats for the Barbary falcons on La Palma. There is a widespread but false idea that these raptors are not native, and that their presence is due to deliberate releases of foreign falcons by local government bodies. Thus, a human-wildlife conflict has arisen with pigeon fanciers whose solution requires more reliable information on the scale of the predation on pigeons and an environmental education campaign.
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